Multilayer container and method for producing recycled polyethylene terephthalate

Abstract

A multilayer container comprising: a polyethylene terephthalate layer comprising polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B); and a gas barrier layer comprising a resin (Y) which is at least one selected from the group consisting of polyethylene furanoate and polyglycolic acid, wherein the phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, with the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer being 0.050-0.220 mass %.

Description

Multilayer container and method for producing recycled polyethylene terephthalate

[0001] The present invention relates to a multilayer container and a method for producing recycled polyethylene terephthalate.

[0002] Polyethylene terephthalate (PET) is characterized by excellent transparency, mechanical properties, melt stability, solvent resistance, aroma retention, recyclability, etc. Therefore, polyethylene terephthalate is widely used in various packaging materials such as films, sheets, and hollow containers. Although polyethylene terephthalate has relatively high gas barrier properties, these properties are not necessarily sufficient for applications requiring better gas barrier properties against oxygen, carbon dioxide, etc. Therefore, methods for improving the gas barrier properties of polyethylene terephthalate have been employed, such as vapor deposition of aluminum oxide or silicon oxide onto molded articles or packaging containers made of polyester resin, or coating, laminating, or melt-mixing a gas barrier resin with high gas barrier properties onto molded articles or packaging containers made of polyethylene terephthalate.

[0003] On the other hand, examples of gas barrier resins include polyamide resins such as nylon 6 and nylon 66, ethylene-vinyl alcohol copolymers, and polyester resins such as polyethylene furanoate (PEF) and polyglycolic acid (PGA). Among polyester resins, PEF and PGA, which use monomers derived from biomass, have excellent gas barrier properties and can reduce the overall weight of the bottle, making them superior to other barrier resins in terms of reducing the environmental impact.

[0004] For example, Patent Document 1 discloses a multilayer container having gas barrier properties made from a carbon-neutral material, which has a layer containing polyethylene furanoate, which is a polycondensate of biomass-derived polyethylene glycol and biomass-derived furandicarboxylic acid.

[0005] However, multilayer polyester containers having a resin layer with barrier properties are more susceptible to yellowing due to heat history than polyethylene terephthalate alone. Therefore, yellowing occurs particularly during the recycling process in which the containers are recovered and the resin is reused. Since this causes a decrease in the commercial value of the packaging container, efforts are being made to suppress yellowing.

[0006] As an example of a container that can improve the color tone of recycled polyethylene terephthalate during recycling, Patent Document 2 discloses a multilayer container having a polyester resin composition layer containing an antioxidant and a polyester resin, and a polyamide resin composition layer containing a specific amount of cobalt salt and a polyamide resin.

[0007] JP 2018-199258 A JP 2018-043773 A

[0008] As described above, multilayer polyester containers having a resin layer with barrier properties tend to yellow, and recycled polyethylene terephthalate obtained by recycling these containers also tends to have a yellowish tinge. Methods for suppressing this yellowing include adding an antioxidant to the container, as described in Patent Document 1, but the colorlessness of the resulting recycled polyethylene terephthalate is still insufficient. Furthermore, recycled polyethylene terephthalate is prone to cloudiness due to the recycling process, and improved transparency is also desired. Therefore, an object of the present invention is to provide a multilayer container that can suppress yellowing of recycled polyethylene terephthalate obtained by recycling multilayer containers and that also has excellent transparency.

[0009] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that a multilayer container having a barrier layer made of a specific polyester and further containing a phenolic antioxidant and a specific phosphorus-based antioxidant in the polyester layer can solve the above-mentioned problems, thereby completing the present invention. The present invention provides the following [1] to

[11] .

[0010] [1] A multilayer container having a polyethylene terephthalate layer containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), and a gas barrier layer containing at least one resin (Y) selected from the group consisting of polyethylene furanoate and polyglycolic acid, wherein the phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is 0.050 to 0.220 mass%. [2] The multilayer container according to [1] above, wherein the content of the phenolic antioxidant (A) in the polyethylene terephthalate layer is 0.010 mass% or more. [3] The multilayer container according to [1] or [2] above, wherein the phosphorus-based antioxidant (B) is a compound represented by the following general formula (1): (In the formula, R 1 ~R 6are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms.) [4] The multilayer container according to any one of [1] to [3] above, wherein the mass ratio [(A) / (B)] of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (B) is 2 / 8 to 5 / 5. [5] The multilayer container according to any one of [1] to [4] above, wherein the content of the gas barrier layer is 0.05 to 15.0 mass% with respect to the total amount of the polyethylene terephthalate layer and the gas barrier layer. [6] The multilayer container according to any one of [1] to [5] above, wherein the biobased content of the gas barrier layer is 90 mass% or more. [7] The multilayer container according to any one of [1] to [6] above, wherein the multilayer container is a hollow container. [8] The multilayer container according to any one of [1] to [7] above, wherein the multilayer container has a 3- to 5-layer structure, the outermost layer and the innermost layer being polyethylene terephthalate layers. [9] A method for producing recycled polyethylene terephthalate, comprising a step of recovering polyethylene terephthalate from the multilayer container according to any one of [1] to [8] above.

[10] A method for producing recycled polyethylene terephthalate according to [9] above, comprising carrying out one or more steps selected from a crystallization step and a solid-state polymerization step after the step of recovering polyethylene terephthalate.

[11] A method for producing recycled polyethylene terephthalate according to [9] or

[10] above, comprising a step of washing the multilayer container according to any one of [1] to [8] above or a pulverized product thereof with an alkaline aqueous solution and recovering polyethylene terephthalate.

[0011] According to the present invention, it is possible to provide a multilayer container in which yellowing of the recycled polyester obtained by recycling a multilayer container can be suppressed and the recycled polyester has excellent transparency.

[0012] [Multilayer Container] The multilayer container of the present invention has a polyethylene terephthalate layer containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), and a gas barrier layer containing at least one resin (Y) selected from the group consisting of polyethylene furanoate and polyglycolic acid, wherein the phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is 0.050 to 0.220 mass%. The reasons why the multilayer container of the present invention can inhibit yellowing of recycled polyethylene terephthalate obtained by recycling and also exhibits excellent transparency are unclear, but are thought to be as follows. If an antioxidant is incorporated into the multilayer container to inhibit yellowing during recycling, the antioxidant in the container may hydrolyze or be washed out during use or cleaning during recycling, making it difficult to fully demonstrate its effects. In the multilayer container of the present invention, the combined use of a phenolic antioxidant and a phosphorus-based antioxidant having a pentaerythritol skeleton and an aromatic ring can suppress the effects of hydrolysis, etc., and it is believed that recycled polyethylene terephthalate with excellent colorlessness and transparency can be obtained even in containers having a gas barrier layer such as polyethylene furanoate or polyglycolic acid.

[0013] <Polyethylene terephthalate layer> The polyethylene terephthalate layer contains polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B). The phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is 0.050 to 0.220% by mass.

[0014] (Polyethylene Terephthalate (X)) The polyethylene terephthalate (PET) (X) contained in the polyethylene terephthalate layer is a polyester mainly having structural units derived from a dicarboxylic acid containing structural units derived from terephthalic acid and structural units derived from a diol containing structural units derived from ethylene glycol. The polyethylene terephthalate (X) preferably has structural units derived from a dicarboxylic acid containing 80 mol% or more of structural units derived from terephthalic acid and structural units derived from a diol containing 80 mol% or more of structural units derived from ethylene glycol, more preferably has structural units derived from a dicarboxylic acid containing 90 mol% or more of structural units derived from terephthalic acid and structural units derived from a diol containing 90 mol% or more of structural units derived from ethylene glycol, and even more preferably has structural units derived from a dicarboxylic acid containing 98 mol% or more of structural units derived from terephthalic acid and structural units derived from a diol containing substantially 100 mol% of structural units derived from ethylene glycol. In this specification, "polyethylene terephthalate (X)" refers to polyethylene terephthalate forming a polyethylene terephthalate layer and polyethylene terephthalate serving as a raw material for the polyethylene terephthalate layer. When simply referring to "polyethylene terephthalate," it refers to polyethylene terephthalate in general, including "polyethylene terephthalate (X)" and recycled polyethylene terephthalate, and the preferred range of "polyethylene terephthalate" in this specification is the same as that of "polyethylene terephthalate (X)."

[0015] Polyethylene terephthalate (X) may contain structural units derived from an aromatic dicarboxylic acid other than terephthalic acid. The aromatic dicarboxylic acid other than terephthalic acid is preferably one or more selected from isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid. These are low cost, and copolymerized polyesters containing these are easy to produce. Among these, isophthalic acid and naphthalenedicarboxylic acid are preferred, with isophthalic acid being more preferred. Polyethylene terephthalate (X) containing structural units derived from isophthalic acid is excellent in moldability and, due to its slow crystallization rate, prevents whitening of molded articles. Furthermore, polyethylene terephthalate (X) containing structural units derived from naphthalenedicarboxylic acid increases the glass transition temperature of the resin, improving heat resistance, and absorbs ultraviolet light, making it suitable for use in the production of multilayer containers that require ultraviolet resistance. Among naphthalenedicarboxylic acids, 2,6-naphthalenedicarboxylic acid is preferred because it is easy to produce and highly economical. When the polyethylene terephthalate (X) contains constituent units derived from an aromatic dicarboxylic acid other than terephthalic acid, the proportion of the constituents derived from an aromatic dicarboxylic acid other than terephthalic acid is preferably 1 to 20 mol %, more preferably 1 to 10 mol %, even more preferably 1 to 5 mol %, and still more preferably 1 to 2 mol %, of the dicarboxylic acid units.

[0016] The polyethylene terephthalate (X) can be produced by a known method such as a direct esterification method or an ester exchange method.

[0017] The intrinsic viscosity of the polyethylene terephthalate (X) is preferably 0.5 to 2.0 dL / g, more preferably 0.6 to 1.5 dL / g. When the intrinsic viscosity is 0.5 dL / g or higher, the resulting container has excellent mechanical properties. The intrinsic viscosity is measured by dissolving the polyethylene terephthalate (X) in a phenol / 1,1,2,2-tetrachloroethane (6 / 4 mass ratio) mixed solvent to prepare 0.2, 0.4, or 0.6 g / dL solutions, and measuring the solutions at 25°C using an automatic viscosity measuring device (Viscotek, manufactured by Malvern Instruments, Inc.). The polyethylene terephthalate (X) may be used singly or in combination of two or more resins.

[0018] (Phenol-based antioxidant (A)) The polyethylene terephthalate layer constituting the multilayer container of the present invention contains a phenol-based antioxidant (A). From the viewpoint of effectively improving the colorlessness and transparency of the recycled polyethylene terephthalate, the content of the phenol-based antioxidant (A) in the polyethylene terephthalate layer is preferably 0.010% by mass or more, more preferably 0.010 to 0.100% by mass, even more preferably 0.011 to 0.050% by mass, and still more preferably 0.011 to 0.030% by mass, and from the viewpoint of transparency in particular, even more preferably 0.012 to 0.022% by mass, and still more preferably 0.013 to 0.018% by mass.

[0019] The phenolic antioxidant (A) is an antioxidant having a phenol structure in which a hydroxyl group is bonded to an aromatic ring in the molecule. The number of phenol structures contained in the molecule is preferably two or more, and more preferably three or more.

[0020] Specific examples of the phenolic antioxidant (A) include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF), 3,9-bis[2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane (Sumilizer GA-80, manufactured by Sumitomo Chemical Co., Ltd.), octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and the like. N,N'-hexane-1,6-diylbis[3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)], 2,4-dimethyl-6-(1-methylpentadecyl)phenol, diethyl [[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphate, 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(octylthiazolinone) methyl)-o-cresol, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamamide), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6 (1H,3H,5H)-trione, 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol, etc. These may be used alone or in combination of two or more. Of these, from the viewpoint of effectively improving the colorless transparency of recycled polyethylene terephthalate, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irganox 1010, manufactured by BASF) is preferred.

[0021] (Phosphorus-Based Antioxidant (B)) The polyethylene terephthalate layer constituting the multilayer container of the present invention contains a phosphorus-based antioxidant (B). The phosphorus-based antioxidant (B) used in the present invention is a compound having a pentaerythritol skeleton and an aromatic ring. From the viewpoint of effectively improving the colorlessness and transparency of the recycled polyethylene terephthalate, the content of the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is preferably 0.030 to 0.210% by mass, more preferably 0.030 to 0.170% by mass, even more preferably 0.033 to 0.150% by mass, and still more preferably 0.033 to 0.090% by mass, based on the entire polyethylene terephthalate layer. From the viewpoint of transparency in particular, it is even more preferably 0.036 to 0.066% by mass, and even more preferably 0.037 to 0.054% by mass.

[0022] In the multilayer container of the present invention, the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is 0.050 to 0.220% by mass, preferably 0.050 to 0.200% by mass, more preferably 0.050 to 0.180% by mass, even more preferably 0.050 to 0.160% by mass, and still more preferably 0.050 to 0.120% by mass, from the viewpoint of transparency in particular, even more preferably 0.050 to 0.088% by mass, and even more preferably 0.050 to 0.072% by mass.

[0023] Furthermore, from the viewpoint of effectively improving the colorless transparency of recycled polyethylene terephthalate, the mass ratio of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (B) [(A) / (B)] is preferably 1 / 9 to 6 / 4, more preferably 1 / 9 to 5 / 5, even more preferably 2 / 8 to 5 / 5, still more preferably 2 / 8 to 4 / 6, and even more preferably 2 / 8 to 3 / 7.

[0024] The phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and may be any compound having a pentaerythritol skeleton and an aromatic ring in the molecule, but is preferably a compound represented by the following general formula (1). The compound represented by the following general formula (1) is a bis(substituted phenyl)pentaerythritol diphosphite. The phosphorus-based antioxidant (B) may be used alone or in combination of two or more. (In the formula, R 1 ~R 6 are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms.

[0025] In formula (1), R 1 and R 4 may be the same or different, but are preferably the same. 2 and R 5 may be the same or different, but are preferably the same. 3 and R 6 may be the same or different, but are preferably the same. 1 and R 4 is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group, more preferably an alkyl group having 4 carbon atoms or a cumyl group, even more preferably a tert-butyl group or a cumyl group, and still more preferably a cumyl group. 2 and R 5 is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group, more preferably an alkyl group having 1 to 3 carbon atoms or a cumyl group, even more preferably a methyl group or a cumyl group, and still more preferably a cumyl group. 3 and R 6 R is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, and is preferably a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a benzyl group, a phenylethyl group, or a cumyl group. 1 and R 4 is a tert-butyl group, R 3 and R6 is preferably a tert-butyl group, and R 1 and R 4 is a cumyl group, R 3 and R 6 is preferably a hydrogen atom.

[0026] Examples of the phosphorus-based antioxidant (B) include bis(nonylphenyl)pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, etc. Among these, from the viewpoint of effectively improving the colorless transparency of recycled polyethylene terephthalate, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite and bis(2,4-dicumylphenyl)pentaerythritol diphosphite are preferred, and from the viewpoint of heat resistance in particular, bis(2,4-dicumylphenyl)pentaerythritol diphosphite is more preferred.

[0027] (Other Components) The polyethylene terephthalate layer may contain other components. Examples of other components include aldehyde catchers, heat stabilizers, light stabilizers, moisture-proofing agents, waterproofing agents, lubricants, and spreading agents. The polyethylene terephthalate layer may contain resins other than the main component polyethylene terephthalate (X), as long as the effects of the present invention are not impaired. The content of polyethylene terephthalate (X) is preferably 80 to 100% by mass, and more preferably 90 to 100% by mass, relative to the total resin amount of the polyethylene terephthalate layer. The resin constituting the polyethylene terephthalate layer may consist solely of polyethylene terephthalate (X).

[0028] (Polyethylene terephthalate resin composition used in polyethylene terephthalate layer) The polyethylene terephthalate layer constituting the multilayer container of the present invention contains polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B). Therefore, when forming the multilayer container, it is preferable to use a polyethylene terephthalate resin composition containing these. Although the method for producing the polyethylene terephthalate resin composition is not limited, it is preferable to produce it by the following method.

[0029] It is preferable to obtain a polyethylene terephthalate resin composition by melt-mixing polyethylene terephthalate (X), the phenol-based antioxidant (A), the phosphorus-based antioxidant (B), and the like.

[0030] The phenolic antioxidant (A), the phosphorus-based antioxidant (B), and other components (additives) may be added to the resin as they are and melt-mixed, or may be dissolved in a liquid component and added to the resin as an additive solution and melt-mixed. Forming them into a solution is preferred because it facilitates metering and addition. Forming them into a solution is also preferred because it allows addition using a dosing system, etc. The additive solution may be added when the masterbatch and polyethylene terephthalate (X) are dry-blended, or may be added after the polyethylene terephthalate (X) is melted.

[0031] The liquid component used in the additive solution is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.5% by mass, relative to the resin (such as polyethylene terephthalate (X)) constituting the polyethylene terephthalate layer. The liquid component used in the additive solution is preferably 0.01 to 1% by mass, more preferably 0.01 to 0.5% by mass, relative to the polyethylene terephthalate (X) constituting the polyethylene terephthalate layer. The liquid component is preferably a liquid resin or a liquid oily component. Examples of the liquid resin include epoxy resins such as epoxidized soybean oil and epoxidized linseed oil, fatty acid polyester resins, polyalkylene glycol resins, polyether ester resins, and acetyl tributyl citrate. Examples of the liquid oily component include vegetable oils such as olive oil, castor oil, jojoba oil, macadamia nut oil, crab rose fruit oil, cacao butter, and lanolin; animal oils such as horse oil, turtle oil, wild boar oil, mink oil, and shark oil; hydrocarbon oils such as petrolatum, liquid paraffin, isodecane, isododecane, octyldodecyl, diisostearyl malate, and hydrogenated polyisobutene; isotridecyl isononanoate, isopropyl isostearate, neopentyl glycol dicaprate, isotridecyl isononanoate, and glycerin diisostearate. Examples of suitable additives include ester oils such as glyceryl triisostearate, diisostearyl malate, octyldodecanol, and di(phytosteryl / 2-octyldodecyl) N-lauroyl-L-glutamate; silicone oils such as dimethylpolysiloxane and phenylmethylpolysiloxane; dimer acid esters, dimer diol derivatives, cholesterol fatty acid esters, phytosterol fatty acid esters, polyglycerin fatty acid esters, pentaerythritol fatty acid esters, and glyceryl tri-2-ethylhexanoate. The method for producing the additive solution is not particularly limited. For example, the additive solution can be obtained by adding the liquid components and various additives, mixing them in a Henschel mixer, tumbler, disperser, or the like, and dispersing them using a Silverson mixer (manufactured by Silverson). In addition to the above, any suitable dispersion device can be used, such as a kneader, roll mill, ball mill, or sand mill.

[0032] Examples of the melt-mixing method include melt blending (melt kneading). Furthermore, when producing a multilayer container as described below, polyethylene terephthalate (X), the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and the like may be dry-blended in advance and melt-mixed in the process of obtaining a multilayer preform. Examples of melt-blending include the masterbatch method and the full compound method, and the masterbatch method is preferred from the viewpoint of preventing deterioration of the resin and the antioxidant.

[0033] The masterbatch method is a method in which a small amount of resin is mixed with a phenolic antioxidant (A), a phosphorus-based antioxidant (B), etc. to form a masterbatch, and then mixed with the remainder of polyethylene terephthalate (X). From the viewpoint of miscibility with polyethylene terephthalate (X), the resin used in the masterbatch is preferably a polyester resin, more preferably polyethylene terephthalate, and even more preferably the same as the remainder of the polyethylene terephthalate (X). The amount of resin used in the masterbatch is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, based on the amount of resin in the entire polyethylene terephthalate resin composition.

[0034] In a method for obtaining a masterbatch, a resin, a phenolic antioxidant (A), a phosphorus-based antioxidant (B), and the like are kneaded together. When the melting point of the resin used in the masterbatch is Tm, the kneading temperature (°C) is preferably Tm+5 to Tm+60, more preferably Tm+10 to Tm+50, and even more preferably Tm+15 to Tm+40, from the viewpoint of sufficient mixing. Specifically, 245 to 300°C is more preferable, 250 to 290°C is even more preferable, and 255 to 280°C is even more preferable. Furthermore, from the viewpoint of sufficient mixing, the kneading time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. Examples of kneading equipment include open-type mixing rolls, closed-type Banbury mixers, kneaders, continuous kneaders (single-screw kneaders, twin-screw kneaders, multi-screw kneaders, etc.), and the like.

[0035] In addition, examples of a method for melt-mixing the masterbatch and the remaining polyethylene terephthalate (X) include melt blending (melt kneading). In addition, when producing a multilayer container as described below, the masterbatch and the remaining polyethylene terephthalate (X) may be dry-blended in advance, and then melt-mixed in the step of obtaining a multilayer preform.

[0036] The full compounding method is a method in which the entire amount of polyethylene terephthalate (X) used in the resin composition is kneaded and mixed with the phenolic antioxidant (A), the phosphorus-based antioxidant (B), and the like. From the viewpoint of sufficient mixing, the kneading temperature is preferably 255 to 310°C, more preferably 265 to 300°C, and even more preferably 270 to 290°C. From the viewpoint of sufficient mixing, the kneading time is preferably 10 to 600 seconds, more preferably 20 to 400 seconds, and even more preferably 30 to 300 seconds. Examples of devices used for kneading include open-type mixing rolls, closed-type Banbury mixers, kneaders, continuous kneaders (single-screw kneaders, twin-screw kneaders, multi-screw kneaders, etc.), and the like.

[0037] <Gas Barrier Layer> The gas barrier layer contains resin (Y) which is at least one selected from the group consisting of polyethylene furanoate (PEF) and polyglycolic acid (PGA). In this specification, "resin (Y)" means "at least one resin selected from the group consisting of polyethylene furanoate (PEF) and polyglycolic acid (PGA)."

[0038] The content of resin (Y) in the gas barrier layer (total of the polyethylene furanoate content and the polyglycolic acid content) is preferably 70 to 100% by mass, based on the total amount of the gas barrier layer, and from the viewpoint of gas barrier properties and suppressing yellowing of recycled polyethylene terephthalate, it is more preferably 90 to 100% by mass, even more preferably 95 to 100% by mass, and still more preferably 99 to 100% by mass. The gas barrier layer may consist of resin (Y) or may consist of resin (Y) alone. The content of resin (Y) contained in the gas barrier layer (total of the polyethylene furanoate content and the polyglycolic acid content) is preferably 0.05 to 15.0% by mass, relative to the total amount of all gas barrier layers and all polyethylene terephthalate layers. From the viewpoints of gas barrier properties and suppressing yellowing of recycled polyethylene terephthalate, it is more preferably 0.5 to 13.0% by mass, even more preferably 1.0 to 12.0% by mass, and even more preferably 2.0 to 11.0% by mass. From the viewpoint of transparency, it is even more preferably 3.0 to 9.0% by mass, and even more preferably 4.0 to 8.0% by mass. Note that when resin (Y) in the gas barrier layer is either polyethylene furanoate or polyglycolic acid, the "total of the polyethylene furanoate content and the polyglycolic acid content" is calculated by treating the other component as 0% by mass. The content of the gas barrier layer is preferably 0.05 to 15.0% by mass relative to the total amount of all gas barrier layers and all polyethylene terephthalate layers. From the viewpoint of gas barrier properties and suppressing yellowing of the recycled polyethylene terephthalate, it is more preferably 0.5 to 13.0% by mass, even more preferably 1.0 to 12.0% by mass, and still more preferably 2.0 to 11.0% by mass. From the viewpoint of transparency, it is even more preferably 3.0 to 9.0% by mass, and still more preferably 4.0 to 8.0% by mass.

[0039] The gas barrier layer contains at least one resin selected from the group consisting of polyethylene furanoate and polyglycolic acid, preferably a resin produced from bio-derived raw materials. The bio-based content of the gas barrier layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 99% by mass or more. There is no upper limit, and it is sufficient as long as it is 100% by mass or less, and 100% by mass is even more preferable. Having a bio-based content within the above range is preferable because the resulting multilayer container can address environmental issues. The bio-based content of the gas barrier layer is the mass ratio of biomass raw materials relative to 100% by mass, the total amount of raw materials contributing to the resin structure contained in the gas barrier layer. From the perspective of increasing the bio-based content of the gas barrier layer, the gas barrier layer preferably contains polyethylene furanoate. For example, polyethylene furanoate can be produced from 2,5-furandicarboxylic acid, which is derived from carbohydrates, and ethylene glycol obtained from plant-derived raw materials.

[0040] (Resin (Y)) Resin (Y) is at least one selected from the group consisting of polyethylene furanoate (PEF) and polyglycolic acid (PGA), and from the viewpoint of gas barrier performance, polyethylene furanoate is preferred.

[0041] Polyethylene furanoate is a polyester having structural units derived from a dicarboxylic acid containing structural units derived from 2,5-furandicarboxylic acid and structural units derived from a diol containing structural units derived from ethylene glycol. The polyethylene furanoate used as resin (Y) is preferably a polycondensate of biomass-derived ethylene glycol and biomass-derived furandicarboxylic acid, and more preferably a compound derived entirely from biomass. The use of such a compound significantly reduces the amount of fossil fuel used and reduces the environmental impact. Biomass-derived furandicarboxylic acid can be produced from glucose, specifically by isomerizing glucose to produce fructose, dehydrating this, alcoholizing, and then oxidizing it. Biomass-derived ethylene glycol is produced from ethanol (biomass ethanol) produced from biomass. For example, biomass-derived ethylene glycol can be obtained by converting biomass ethanol to ethylene oxide using a conventional method, or by other methods to produce ethylene glycol.

[0042] The polycondensation of furandicarboxylic acid and ethylene glycol can be carried out by a conventionally known method. Specifically, the polycondensation can be carried out by a general melt polymerization method in which esterification and / or transesterification of furandicarboxylic acid and ethylene glycol is carried out, followed by a polycondensation reaction under reduced pressure, or by a known solution heating dehydration condensation method using an organic solvent. The polycondensation reaction is preferably carried out in the presence of a polymerization catalyst. The timing of adding the polymerization catalyst is not particularly limited as long as it is before the polycondensation reaction, and it may be added when the raw materials are charged or when the pressure reduction begins.

[0043] The polymerization catalyst generally includes a compound containing a metal element of Groups 1 to 14 of the periodic table, excluding hydrogen and carbon. Specific examples include compounds containing an organic group, such as a carboxylate, alkoxy salt, organic sulfonate, or β-diketonate salt, containing at least one metal selected from the group consisting of titanium, zirconium, tin, antimony, cerium, germanium, zinc, cobalt, manganese, iron, aluminum, magnesium, calcium, strontium, sodium, and potassium, as well as inorganic compounds, such as oxides and halides of the above metals, and mixtures thereof. Furthermore, the content of polyethylene furanoate in the multilayer container is preferably 0.05 to 15.0% by mass, based on the total amount of all gas barrier layers and all polyethylene terephthalate layers. From the viewpoints of gas barrier properties and suppressing yellowing of the recycled polyethylene terephthalate, it is more preferably 0.5 to 13.0% by mass, even more preferably 1.0 to 12.0% by mass, even more preferably 2.0 to 11.0% by mass, even more preferably 3.0 to 9.0% by mass, and even more preferably 4.0 to 8.0% by mass. This further improves the gas barrier properties of the multilayer container. It also further improves the recyclability of the multilayer container after use. The polyethylene furanoate may be used alone, or two or more types may be used in combination. The intrinsic viscosity of the polyethylene furanoate is preferably 0.5 to 2.0 dL / g, more preferably 0.6 to 1.5 dL / g. An intrinsic viscosity of 0.5 dL / g or higher results in excellent mechanical properties of the container. The intrinsic viscosity is measured by dissolving polyethylene furanoate in a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (6 / 4 mass ratio) to prepare 0.2, 0.4, and 0.6 g / dL solutions, and measuring the solutions at 25°C using an automatic viscosity measuring device (Viscotek, manufactured by Malvern Instruments, Inc.). The glass transition temperature of polyethylene furanoate is preferably 75 to 95°C, and more preferably 80 to 90°C.

[0044] Polyglycolic acid is a polymer of glycolic acid and contains the structural unit [—O—CH2—CO—] derived from glycolic acid. The proportion of the structural unit is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass. Other structural units besides the structural unit include [—O—(CH2) n -O-CO-(CH2) m -CO-] (where n = 1 to 10, m = 0 to 10), [-O-CH(CH2) j H—CO—] (where j=1 to 10), [—O—(CR 7 R 8 ) k -CO-] (where R 7 , R 8 are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms (k = 2 to 10), [—O—CH2—CH2—CH2—O—CO—], [—O—CH2—O—CH2—CH2—], etc., and the melting point, molecular weight, viscosity, etc. of the polyglycolic acid can be adjusted by using these structural units. The polyglycolic acid used as resin (Y) is preferably a polymer of glycolic acid derived from biomass, and more preferably a compound derived entirely from biomass. The use of such a compound can significantly reduce the amount of fossil fuel used and reduce the environmental burden. Biomass-derived glycolic acid can be produced from plant biomass. Specifically, it can be produced by using glucose obtained by hydrolysis of cellulosic biomass as a raw material, via fermentation or chemical conversion processes. For example, methods include directly producing glycolic acid by anaerobic fermentation of glucose, or producing glycolic acid from glucose via lactic acid.

[0045] Polyglycolic acid can be produced by known methods, such as condensation polymerization of glycolic acid or glycolic acid esters, and ring-opening polymerization of glycolide.

[0046] The glass transition temperature of polyglycolic acid is preferably 30 to 45° C., more preferably 35 to 40° C., the melting point is preferably 215 to 230° C., more preferably 220 to 225° C., and the crystallization temperature is preferably 60 to 100° C., more preferably 80 to 95° C., and even more preferably 85 to 95° C. These temperatures are measured in accordance with JIS K7121:2012.

[0047] (Other Components) The gas barrier layer may contain other components. Examples of other components include oxygen absorbers, carbon dioxide absorbers, plasticizers, UV stabilizers, color inhibitors, matting agents, deodorizers, flame retardants, weathering agents, antistatic agents, thread friction reducers, slip agents, mold release agents, antioxidants, ion exchange agents, dispersants, UV absorbers, acetaldehyde absorbers (e.g., AA Scavengers manufactured by Color Matrix), color pigments, heat stabilizers, light stabilizers, moisture-proofing agents, waterproofing agents, lubricants, and spreading agents. Examples of oxygen absorbers include iron-based oxygen absorbers and non-iron-based oxygen absorbers. Non-iron-based oxygen absorbers are more preferred because they can maintain the transparency of the container body. Examples of iron-based oxygen absorbers include iron powders such as reduced iron powder, interfacial iron powder, atomized iron powder, iron grinding powder, electrolytic iron powder, and pulverized iron. Examples of non-iron-based oxygen absorbers include ethylenically unsaturated group-containing copolymers. Examples of the ethylenically unsaturated group-containing copolymer include polydienes such as polybutadiene, polychloroprene, poly(2-ethylbutadiene), and poly(2-butylbutadiene) polymerized mainly at the 1,4-positions; ring-opening metathesis polymers of cycloolefins such as polyoctenylene, polypentenylene, and polynorbornene; and styrene-diene block copolymers such as styrene-isoprene block copolymers, styrene-butadiene copolymers, and styrene-isoprene-styrene block copolymers.

[0048] The gas barrier layer may contain a resin other than the main component resin (Y), as long as the effects of the present invention are not impaired. Examples of such resins include polyester resins, (meth)acrylic resins, polyolefin resins, vinyl resins, cellulose resins, nylon resins, phenolic resins, polyurethane resins, epoxy resins, and ionomer resins. The content of resin (Y) is preferably 80 to 100 mass %, and more preferably 90 to 100 mass %, relative to the total resin amount in the gas barrier layer. The resin constituting the gas barrier layer may consist solely of resin (Y).

[0049] <Structure and Properties of Multilayer Container> The multilayer container of the present invention has a polyethylene terephthalate layer containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), and a gas barrier layer containing at least one resin (Y) selected from the group consisting of polyethylene furanoate and polyglycolic acid, wherein the phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is 0.050 to 0.220 mass%. The multilayer container of the present invention may contain a resin layer other than the polyethylene terephthalate layer and the gas barrier layer. However, from the viewpoints of facilitating separation during recycling and improving the color tone of the container and the recovered polyethylene terephthalate, it is preferable that the content of the resin layer other than the polyethylene terephthalate layer and the gas barrier layer is low, and it is preferable that the multilayer container is substantially free of resin layers other than the polyethylene terephthalate layer and the gas barrier layer. In addition, an adhesive layer made of an adhesive or an inorganic layer made of an inorganic material may be provided, but from the viewpoint of facilitating separation during recycling and improving the yellowing suppression effect, it is preferable that the content of the adhesive layer or inorganic layer is small, and it is preferable that the adhesive layer or inorganic layer is substantially not included.

[0050] The multilayer container of the present invention has a multilayer structure of two or more layers, preferably a 2- to 5-layer structure, more preferably a 3- to 5-layer structure, even more preferably a 3-layer structure or a 5-layer structure, and even more preferably a 3-layer structure. The outermost layer of the multilayer container of the present invention is preferably a polyethylene terephthalate layer. The innermost layer is also preferably a polyethylene terephthalate layer, and more preferably the outermost and innermost layers are polyethylene terephthalate layers. When the outermost layer is a polyethylene terephthalate layer, the multilayer container has excellent impact resistance, appearance, and design. Therefore, the structure of the multilayer container is preferably a 2- to 5-layer structure with the outermost layer being a polyethylene terephthalate layer, and more preferably a 3- to 5-layer structure with the outermost and innermost layers being polyethylene terephthalate layers.

[0051] In the case of a two-layer structure, from the innermost layer, it is preferable that the structure be gas barrier layer / polyethylene terephthalate layer; in the case of a three-layer structure, from the innermost layer, it is preferable that the structure be polyethylene terephthalate layer / gas barrier layer / polyethylene terephthalate layer; and in the case of a five-layer structure, from the innermost layer, it is preferable that the structure be polyethylene terephthalate layer / gas barrier layer / polyethylene terephthalate layer / gas barrier layer / polyethylene terephthalate layer.

[0052] The multilayer container of the present invention is preferably a hollow container. When the multilayer container is a hollow container, at least the body portion has a multilayer structure. The ratio of the thickness (W) of the polyethylene terephthalate layer in the body portion to the thickness (S) of the gas barrier layer (thickness ratio W / S) is preferably 2.5 or more and 200 or less. The thickness of the polyethylene terephthalate layer refers to the average thickness. When the body portion contains multiple polyethylene terephthalate layers, the thicknesses of the multiple layers are averaged to determine the average thickness per layer. The same applies to the thickness of the gas barrier layer. A thickness ratio W / S of 2.5 or more is preferable because it facilitates separation of the resin (Y) from the polyethylene terephthalate during the separation process, particularly winnowing and gravity separation, in the production process of recycled polyethylene terephthalate. Furthermore, a thickness ratio W / S of 200 or less provides excellent gas barrier properties for the hollow container, allowing the contents to be stored for a long period of time. From the viewpoint of improving the gas barrier properties of the hollow container while increasing the separability in the separation step, the thickness ratio (W / S) is more preferably 3 to 50, and even more preferably 4 to 15.

[0053] Furthermore, when the multilayer container is a hollow container, the total thickness of the body of the hollow container (i.e., the total thickness of all layers in the body) is preferably 100 μm to 5 mm, more preferably 150 μm to 3 mm, and even more preferably 200 μm to 2 mm. Furthermore, the thickness (W) of each polyethylene terephthalate layer is preferably 30 μm to 2 mm, more preferably 40 μm to 1 mm, and even more preferably 50 μm to 500 μm. The thickness (S) of each gas barrier layer is preferably 1 to 200 μm, more preferably 3 to 100 μm, and even more preferably 8 to 50 μm. In the present invention, by setting the thickness of the gas barrier layer within this range, gas barrier properties are ensured, and the gas barrier layer is easily separated from the polyethylene terephthalate in the separation step.

[0054] When the multilayer container of the present invention is a hollow container, it is more preferably a liquid packaging container that is used by filling the interior of the hollow container with a liquid, and even more preferably a beverage packaging container. Examples of liquids that can be filled include beverages, liquid seasonings, chemicals, pharmaceuticals, detergents, etc., and beverages that can be effectively prevented from deteriorating due to oxygen by the multilayer container of the present invention are preferred. Examples of beverages include water, carbonated water, oxygenated water, hydrogenated water, milk, dairy products, juice, coffee, coffee drinks, carbonated soft drinks, tea, and alcoholic beverages. Examples of liquid seasonings include sauces, soy sauce, syrup, mirin, dressings, etc. Examples of chemicals include pesticides and insecticides.

[0055] <Method for manufacturing multilayer container> The method for manufacturing a multilayer container of the present invention is not particularly limited as long as it is a method for manufacturing a multilayer container having a polyethylene terephthalate layer containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), and a gas barrier layer containing resin (Y) which is at least one selected from the group consisting of polyethylene furanoate and polyglycolic acid, but is preferably a manufacturing method including the following steps 1 and 2. In other words, the method for manufacturing a multilayer container of the present invention is preferably a method including the following steps 1 and 2, and for manufacturing a multilayer container having a polyethylene terephthalate layer containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), and a gas barrier layer containing resin (Y) which is at least one selected from the group consisting of polyethylene furanoate and polyglycolic acid. Step 1: A step of coinjection molding a resin (Y) used in a gas barrier layer, a gas barrier resin composition containing the resin (Y), or a gas barrier resin mixture containing the resin (Y), with a polyethylene terephthalate resin composition containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B), or a polyethylene terephthalate resin mixture containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B) to obtain a multilayer preform. Step 2: A step of blow molding the multilayer preform.

[0056] (Step 1 (Step of Obtaining a Multilayer Preform)) In step 1, resin (Y), a gas barrier resin composition containing resin (Y), or a gas barrier resin mixture containing resin (Y), and the polyethylene terephthalate resin composition or the polyethylene terephthalate resin mixture are co-injection molded to obtain a multilayer preform. The gas barrier resin composition is a composition containing at least one resin (Y) selected from the group consisting of polyethylene furanoate and polyglycolic acid as a main component, and containing resins other than polyethylene furanoate and polyglycolic acid, and other components, etc., as described in the section <Gas Barrier Layer>. The polyethylene terephthalate resin composition is a composition containing polyethylene terephthalate (X) as a main component, and containing a phenolic antioxidant (A) and a phosphorus-based antioxidant (B), and may contain resins other than polyethylene terephthalate (X), and other components, etc., as described in the section <Polyethylene Terephthalate Layer>. The gas barrier resin mixture refers to a mixture obtained by dry-blending resin (Y), a resin other than resin (Y), and other components, or a mixture obtained by dry-blending a masterbatch containing other components with the remainder of resin (Y). These gas barrier resin mixtures become the gas barrier resin composition by melt-mixing the components in this process. The polyethylene terephthalate resin mixture refers to a mixture obtained by dry-blending polyethylene terephthalate (X), a phenolic antioxidant (A), a phosphorus-based antioxidant (B), a resin other than polyethylene terephthalate (X), and other components, or a mixture obtained by dry-blending a masterbatch containing the phenolic antioxidant (A), the phosphorus-based antioxidant (B), a resin other than polyethylene terephthalate (X), and other components with the remainder of polyethylene terephthalate (X). These polyethylene terephthalate resin mixtures become the polyethylene terephthalate resin composition by melt-mixing the components in this process. In co-injection molding, the polyethylene terephthalate resin composition or polyethylene terephthalate resin mixture and resin (Y) (resin, resin composition, or resin mixture) are each extruded into a mold and co-injected to form a multilayer preform.

[0057] (Step 2 (Blow Molding Step)) In Step 2, the multilayer preform is blow molded. In the method for producing a multilayer container of the present invention, it is preferable to mold the multilayer preform (multilayer parison) obtained in Step 1 by stretch blow molding. Among these, in Step 2, it is preferable to stretch blow mold the multilayer preform obtained by coinjection molding, and it is more preferable to biaxially stretch blow mold the multilayer preform obtained by coinjection molding. Note that the conditions for biaxial stretch blow molding are preferably a preform heating temperature of 95 to 110°C, a primary blow pressure of 0.5 to 1.2 MPa, and a secondary blow pressure of 2.0 to 2.6 MPa. This suppresses the occurrence of thickness unevenness and stretch unevenness, and makes it possible to obtain a multilayer container with excellent strength.

[0058] [Method for producing recycled polyethylene terephthalate] The method for producing recycled polyethylene terephthalate of the present invention is a method for producing recycled polyethylene terephthalate, which includes a step of recovering polyethylene terephthalate from the multilayer container. The method for producing recycled polyethylene terephthalate of the present invention will be described in detail below.

[0059] In this manufacturing method, used multilayer containers are usually used, but unused containers may also be used. Examples of used multilayer containers include those that have been once distributed on the market and then recovered. In this manufacturing method, if a lid is attached to the multilayer container, it is preferable to first remove the lid from the multilayer container. Next, the container is crushed, and if necessary, polyethylene terephthalate is selectively extracted and separated, and recovered as recycled polyethylene terephthalate (recovery step). In the recovery step, it is preferable to wash the container or the crushed material with an alkaline aqueous solution (washing step). Next, if necessary, granulation is performed to form pellets (granulation step). Furthermore, if necessary, a crystallization step and a solid-state polymerization step are performed (crystallization / solid-state polymerization step). Each step is described below.

[0060] <Washing Step> In the method for producing recycled polyethylene terephthalate of the present invention, it is preferable to wash the multilayer container or its pulverized product with an alkaline aqueous solution to recover polyethylene terephthalate. Washing with an alkaline aqueous solution can efficiently remove not only the contents stored in the multilayer container but also adhesives and the like. Washing with an alkaline aqueous solution may be performed on the container as is, simultaneously with pulverization, or after pulverization, or after separation into polyethylene terephthalate and the resin (Y) (polyethylene furanoate and / or polyglycolic acid) that constitutes the gas barrier layer. Furthermore, washing may be performed multiple times. Washing is preferably performed after pulverization, but for convenience, the washing step will be described before the description of the recovery step described below.

[0061] The solvent for the alkaline aqueous solution used to wash the multilayer container or its pulverized product is water in terms of cleaning efficiency and cost. In addition to water, the solution may contain an aqueous organic solvent. Examples of the aqueous organic solvent include lower alcohols such as methanol, ethanol, and isopropyl alcohol, and diols. The pH of the alkaline aqueous solution is preferably 8 or higher, more preferably 10 or higher, and even more preferably 12 or higher. There is no upper limit, but it is preferably 14 or lower. The alkaline aqueous solution contains an alkaline substance in addition to the solvent. The alkaline substance is preferably at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides, and from the standpoints of cleaning efficiency and cost, alkali metal hydroxides are more preferred. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. From the standpoints of cleaning efficiency and cost, at least one selected from the group consisting of sodium hydroxide and potassium hydroxide is preferred, and sodium hydroxide is more preferred. The content of the alkaline substance is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and even more preferably 1 to 5% by mass, based on the total amount of the alkaline aqueous solution.

[0062] Any type of washing device may be used, but it is preferable to use a container equipped with a stirrer, especially when washing pulverized material. The temperature during washing is preferably 30 to 95°C, more preferably 50 to 90°C, and even more preferably 70 to 90°C. The washing time is preferably 5 minutes to 10 hours, 5 minutes to 1 hour, or 10 to 30 minutes. The washing temperature and washing time can be appropriately selected depending on the amount and shape of the multilayer container or the pulverized material, etc.

[0063] The method for producing recycled polyethylene terephthalate of the present invention includes a washing step of washing with an alkaline aqueous solution, but may also include a step of washing with a liquid other than an alkaline aqueous solution. Preferably, washing with water is further carried out. After washing, it is preferable to heat and dry the recycled polyethylene terephthalate as needed. By carrying out the drying step, the water content of the recycled polyethylene terephthalate obtained by this method can be reduced, making it possible to provide high-quality recycled polyethylene terephthalate with high thermal stability. The drying step can be carried out using, for example, air blown by a dryer or hot air.

[0064] <Recovery Step> The recovery step is a step of crushing the multilayer container to recover the polyethylene terephthalate. In particular, it is preferable to crush the multilayer container and then remove all or part of the gas barrier layer to selectively extract the polyethylene terephthalate, and it is more preferable to separate the polyethylene terephthalate from the resin (Y) constituting the gas barrier layer. The crushing of the multilayer container can be carried out using a crusher such as a single-axis crusher, a biaxial crusher, a triaxial crusher, or a cutter mill. The crushed material obtained by crushing is, for example, in the form of flakes, powder, or lumps. However, since the majority of the multilayer container has a thin multilayer laminate structure with a thickness of several mm or less, such as the body, the majority of the crushed material is usually in the form of flakes. Note that a crushed material in the form of flakes refers to a thin or flat material with a thickness of about 2 mm or less.

[0065] Furthermore, in multilayer containers, the polyethylene terephthalate layer and the gas barrier layer are structurally integrated, but they are not usually adhered to each other, and in the pulverization process, the polyethylene terephthalate and resin (Y) are easily separated as separate pulverized materials. Furthermore, by forming them into flakes, they are easily separated by the air current during the winnowing separation process described below. However, the polyethylene terephthalate and resin (Y) are not necessarily completely separated in the pulverization process, and the pulverized material is separated into one with a relatively high polyethylene terephthalate content and one with a relatively low polyethylene terephthalate content and a relatively high total resin (Y) content. Hereinafter, for convenience of explanation, the one with a relatively high polyethylene terephthalate content will be simply referred to as polyethylene terephthalate, and the one with a relatively high resin (Y) content will be simply referred to as resin (Y).

[0066] As described above, the crushed material is separated into polyethylene terephthalate and resin (Y) (separation step). The separation method preferably uses specific gravity separation, which takes advantage of the difference in specific gravity between polyethylene terephthalate and resin (Y). That is, the gas barrier layer is preferably removed by winnowing after crushing the multilayer container. Specific examples of specific gravity separation include winnowing, which separates crushed material using wind power. Winnowing, for example, involves separating crushed material exposed to the airflow generated by a separator capable of generating a rotating airflow inside, into material with a high specific gravity or a small specific surface area that falls naturally under its own weight and material with a low specific gravity or a large specific surface area that is lifted up by the airflow. In this method, crushed polyethylene terephthalate material falls naturally under its own weight, while crushed resin (Y) material is lifted up, thereby enabling the polyethylene terephthalate and resin (Y) to be separated and recovered. In this type of winnowing, the same operation may be repeated on the same crushed material. For example, the naturally fallen material may be further subjected to winnowing to increase the content of polyethylene terephthalate in the recycled polyethylene terephthalate. Note that the separation method is not limited to winnowing, and examples include a method in which the crushed material is immersed in a liquid such as water and separated based on the difference in specific gravity of the crushed material relative to the liquid, and a method in which the crushed material is subjected to a certain amount of vibration to separate and separate crushed material having different specific gravities.

[0067] <Granulation Process> The recovered recycled polyethylene terephthalate is preferably granulated into pellets to facilitate handling during molding and other processes. Granulation may be performed before or after the crystallization / solid-state polymerization process described below, but is preferably performed before the crystallization / solid-state polymerization process. Performing granulation before the crystallization / solid-state polymerization process also improves handling during the crystallization / solid-state polymerization process. In the granulation process, the pulverized material is preferably plasticized and granulated by melt blending. Granulation devices for plasticization and granulation include single-screw extruders, twin-screw extruders, and multi-screw extruders, but any known device can be used. The pellets are preferably cylindrical, spherical, or elliptical. For example, granulation is preferably performed by extruding the plasticized recycled polyethylene terephthalate into strands, cooling them in a water bath, and cutting them into pellets using a pelletizer. The pellets removed from the water bath are usually dried to remove moisture from their surfaces.

[0068] <Crystallization / Solid-State Polymerization Step> After the step of recovering polyethylene terephthalate, it is preferable to carry out one or more steps selected from a crystallization step and a solid-state polymerization step, and it is more preferable to carry out both the crystallization step and the solid-state polymerization step. The crystallization / solid-state polymerization step is preferably carried out on the pelletized polyethylene terephthalate described above, but may also be carried out on an unpelletized material (e.g., a pulverized product). When both crystallization and solid-state polymerization are carried out, it is preferable to crystallize the polyethylene terephthalate and then carry out solid-state polymerization. The crystallization of polyethylene terephthalate is carried out by maintaining the polyethylene terephthalate under a constant heating condition. The crystallization is preferably carried out by heating the polyethylene terephthalate at, for example, 100 to 230°C. Crystallization of polyethylene terephthalate prevents the polyethylene terephthalate from fusing together or adhering to the inner surfaces of equipment during solid-state polymerization or molding.

[0069] Solid-state polymerization is preferably carried out by maintaining a temperature equal to or higher than (the melting point of polyethylene terephthalate - 80°C) and lower than the melting point of polyethylene terephthalate for a certain period of time. By maintaining the temperature below the melting point, melting of the polyethylene terephthalate is prevented, and for example, the polyethylene terephthalate is prevented from adhering to the surface of the apparatus, which would reduce work efficiency. Furthermore, by maintaining the temperature at or higher than (the melting point of polyethylene terephthalate - 80°C), polymerization proceeds at a sufficient rate, making it easier to obtain the desired physical properties. Here, "(the melting point of polyethylene terephthalate - 80°C)" means "a temperature 80°C lower than the melting point of polyethylene terephthalate."

[0070] Solid-state polymerization may be carried out under vacuum or in an inert gas stream such as nitrogen or argon. When carried out under vacuum, the pressure is preferably 1.0 torr or less, more preferably 0.5 torr or less, and even more preferably 0.1 torr or less. In addition, whether under vacuum or in an inert gas stream such as nitrogen or argon, it is preferable to reduce the oxygen concentration remaining in the system as much as possible, and the oxygen concentration is preferably 300 ppm or less, more preferably 30 ppm or less. By keeping the oxygen concentration at 30 ppm or less, poor appearance such as yellowing is less likely to occur. When solid-state polymerization is carried out under vacuum, it is preferable to maintain uniform heat transfer by constantly repeating stirring or mixing of the polyethylene terephthalate. When carried out in the presence of an inert gas, it is preferable to always keep the surface of the polyethylene terephthalate in contact with the dry gas under a dry gas stream.

[0071] Examples of solid-state polymerization apparatuses for carrying out the crystallization / solid-state polymerization step include tumbler-type batch apparatuses equipped with a heating jacket, drying silo-type apparatuses equipped with an inert gas flow system, and crystallization apparatuses and reactors equipped with an internal stirring blade and discharge screw. It is preferable that crystallization and solid-state polymerization are carried out continuously or simultaneously in the same apparatus. The heating time for solid-state polymerization is determined appropriately taking into account the apparatus and other conditions, as long as it is a time that allows polyethylene terephthalate to obtain sufficient physical properties. Since solid-state polymerization involves maintaining polyethylene terephthalate at high temperatures for a long period of time, the presence of impurities in the polyethylene terephthalate may deteriorate its quality, such as color tone. It is preferable that most of the resin (Y) used in the gas barrier layer is removed in the removal step described above. In this case, deterioration in quality that may occur during solid-state polymerization is minimized.

[0072] When the method for producing recycled polyethylene terephthalate includes a step of removing resin (Y), the total content of polyethylene furanoate and polyglycolic acid as resin (Y) in the obtained recycled polyethylene terephthalate is preferably less than 1 mass%, more preferably less than 0.8 mass%, and even more preferably less than 0.6 mass%. In this way, by reducing the content of resin (Y), the quality of the recycled polyethylene terephthalate is improved. Furthermore, in the method for producing recycled polyethylene terephthalate of the present invention, steps other than the steps described above may be carried out.

[0073] The recycled polyethylene terephthalate obtained by this production method can be used for various purposes such as resin moldings and fibers.

[0074] EXAMPLES The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples.

[0075] [Raw Materials] The polyethylene terephthalate, polyethylene furanoate, polyglycolic acid, and antioxidant used in the Examples and Comparative Examples are as follows: <Polyethylene terephthalate> PET 1101: Polyclear Refresh PET 1101, polyethylene terephthalate (manufactured by Indorama)

[0076] <Polyethylene furanoate> PEF: Polyethylene furanoate (the polyethylene furanoate produced in Production Example 1 below was used. Glass transition temperature: 86°C, intrinsic viscosity: 0.67 dL / g, oxygen permeability: 0.33 cc mm / m ２ ・day・ATM)

[0077] Production Example 1 (Production of Polyethylene Furanoate) 1.5 kg of furandicarboxylic acid and 1.5 kg of ethylene glycol were weighed into a production apparatus equipped with a packed column-type rectification column, a partial condenser, a total condenser, a cold trap, a stirrer, a heating device, and a nitrogen inlet tube, and the temperature was raised to 200°C under a nitrogen flow rate and allowed to stand for 1.5 hours. Thereafter, zinc acetate was added in an amount to give 400 ppm, calculated as zinc, relative to the total raw materials, and the temperature was gradually raised to 260°C while gradually reducing the pressure to 0.1 kPa. After 4 hours, nitrogen was again introduced and the mixture was cooled, yielding polyethylene furanoate.

[0078] <Polyglycolic acid> PGA: Polyglycolic acid (the polyglycolic acid produced in Production Example 2 below was used. Glass transition temperature: 38°C, melting point: 221°C, oxygen permeability: 0.03 cc mm / m ２ ・day・ATM)

[0079] Production Example 2 (Production of Polyglycolic Acid) 3 kg of glycolide and tin dichloride dihydrate (30 ppm relative to glycolide) were weighed into a sealable production apparatus, heated to 170° C., and allowed to stand for 7 hours. The resulting bulk polymer was pulverized, and then 0.03 parts by mass of a phosphite-based antioxidant (ADK STAB PEP8) was added relative to 100 parts by mass of the polymer. The mixture was melt-kneaded in a twin-screw extruder to obtain the target polyglycolic acid.

[0080] The glass transition temperature, melting point, and oxygen permeability of polyethylene furanoate and polyglycolic acid were measured as follows: (Glass Transition Temperature of Polyethylene Furanoate) The glass transition temperature (Tg) was measured using a differential scanning calorimeter (DSC, Shimadzu Corporation, DSC-60) by heating in a nitrogen stream from room temperature to 260°C at a heating rate of 10°C / min, immediately cooling to below room temperature, and again heating from room temperature to 260°C at a heating rate of 10°C / min.

[0081] (Oxygen Permeability of Polyethylene Furanoate) Polyethylene furanoate was fed into a single-screw extruder equipped with a T-die (manufactured by Plastics Engineering Research Institute, screw diameter 30 mm), melt-extruded from the die at an extrusion temperature of 260°C, and cooled with a cast roll at a temperature of 80°C to obtain a monolayer unstretched film having a width of 175 mm and a thickness of 50 μm. The oxygen permeability (OTR, unit: cc / m) of the obtained monolayer unstretched film was measured using an oxygen permeability measuring device (manufactured by MOCON, "OX-TRAN (registered trademark) 2 / 21") by the isobaric method in an atmosphere of 23°C and a relative humidity (RH) of 60%. ２ The oxygen permeability coefficient (unit: cc mm / m) was calculated from the film thickness of the sample. ２ The pressure of the oxygen atmosphere was 1 atm, and the measurement time was 24 hours (1 day).

[0082] (Glass Transition Temperature and Melting Point of Polyglycolic Acid) The glass transition temperature (Tg) and melting point (Tm) were measured using a differential scanning calorimeter (DSC, DSC-60 manufactured by Shimadzu Corporation) by heating in a nitrogen stream from room temperature to 240°C at a heating rate of 10°C / min, immediately cooling to below room temperature, and again heating from room temperature to 240°C at a heating rate of 10°C / min.

[0083] (Oxygen permeability of polyglycolic acid) Polyglycolic acid was supplied to a single-screw extruder equipped with a T-die (manufactured by Plastics Engineering Research Institute, screw diameter 30 mm), melt-extruded from the die at an extrusion temperature of 240°C, and cooled with a cast roll at a temperature of 35°C to obtain a monolayer unstretched film having a width of 175 mm and a thickness of 50 µm. The oxygen permeability (OTR, unit: cc / m) of the obtained monolayer unstretched film was measured using an oxygen permeability measuring device (manufactured by MOCON, "OX-TRAN (registered trademark) 2 / 21") by the isobaric method in an atmosphere of 23°C and a relative humidity (RH) of 60%. ２ The oxygen permeability coefficient (unit: cc mm / m) was calculated from the film thickness of the sample. ２ The pressure of the oxygen atmosphere was 1 atm, and the measurement time was 24 hours (1 day).

[0084] <Phenol-based antioxidants (A)> Irganox 1010: Pentaerythritol Tetrakis[3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate] (trade name: Irganox 1010, manufactured by BASF) <Phosphorus-based antioxidants (phosphorus-based antioxidants (B) and phosphorus-based antioxidants other than (B))> Doverphos S9228: Bis(2,4-di-cumylphenyl)pentaerythritol diphosphite (trade name: Doverphos S9228, manufactured by Dover Chemical Co., phosphorus-based antioxidant (B)) PEP-36: Bis(2,6-di-ter-butyl-4-methylphenyl)pentaerythritol-diphosphite (trade name: Adekastab PEP-36, manufactured by ADEKA Corporation, phosphorus-based antioxidant (B)) PEP-8: O,O'-Dioctadecylpentaerythritol bis(phosphite) (a phosphorus-based antioxidant having a pentaerythritol skeleton but not an aromatic ring, trade name: Adekastab PEP-8, manufactured by ADEKA Corporation, a phosphorus-based antioxidant other than (B)) Irgafos 168: Tris(2,4-di-tert-butylphenyl)phosphite (a phosphorus-based antioxidant having an aromatic ring but not a pentaerythritol skeleton, trade name: Irgafos 168, manufactured by BASF, a phosphorus-based antioxidant other than (B))

[0085] Example 1 [Production of multilayer container and recycled polyethylene terephthalate] <1. Production of polyethylene terephthalate resin mixture> A polyethylene terephthalate resin mixture was obtained by dry-blending in advance 99.94 parts by mass of polyethylene terephthalate (Polyclear Refresh PET 1101), 0.0150 parts by mass of Irganox 1010 as a phenolic antioxidant (A) (150 ppm in the polyethylene terephthalate layer), and 0.0450 parts by mass of Doverphos S9228 as a phosphorus-based antioxidant (B) (450 ppm in the polyethylene terephthalate layer).

[0086] 2. Production of Multilayer Containers (Preform Molding) Using an injection molding machine (Sumitomo Heavy Industries, Ltd., Model DU130CI) with two injection cylinders and a two-cavity mold (Kortec), polyethylene furanoate was injected from one injection cylinder and the polyethylene terephthalate resin mixture from the other injection cylinder. A three-layer preform (equivalent to 25 g per preform) consisting of a polyethylene terephthalate layer / gas barrier layer (polyethylene furanoate layer) / polyethylene terephthalate layer was injection molded under the conditions shown below, with the mass proportions of the polyethylene terephthalate layer and the gas barrier layer being as shown in Table 1. The preform had a total length of 95 mm, an outer diameter of 22 mm, and a wall thickness of 4.0 mm. The three-layer preform molding conditions were as shown below. Skin side injection cylinder temperature: 285°C Core side injection cylinder temperature (3 layers only): 265°C Mold resin flow path temperature: 285°C Mold cooling water temperature: 15°C Cycle time: 40 seconds

[0087] (Bottle Molding) The preform obtained in the (Preform Molding) step was biaxially stretched and blow molded using a blow molding machine (EFB1000ET, manufactured by Frontier) to obtain a bottle (hollow multilayer container). The bottle had a total length of 223 mm, an outer diameter of 65 mm, an internal volume of 500 mL, and a petaloid bottom. No dimples were provided on the body. The biaxial stretch blow molding conditions were as follows: Preform heating temperature: 103°C, stretch rod pressure: 0.7 MPa, primary blow pressure: 1.1 MPa, secondary blow pressure: 2.5 MPa, primary blow delay time: 0.30 seconds, primary blow time: 0.30 seconds, secondary blow time: 2.0 seconds, blow exhaust time: 0.6 seconds, mold temperature: 30°C.

[0088] <3. Production of Recycled Polyethylene Terephthalate> (Washing, Recovery, and Granulation Process) 10 kg of the hollow multilayer containers obtained in <2. Production of Multilayer Containers> above were crushed using a crusher with a mesh size of 10 mm. Each kg of the resulting crushed flakes was placed in a container equipped with a stirrer, and 4 L of 1% sodium hydroxide aqueous solution was added. The mixture was washed while stirring. The washing temperature was 85°C, and the washing time was 15 minutes. After removing the washing water, the crushed material was placed in 45°C water in an amount four times the mass of the crushed material and stirred for 5 minutes. After dehydration, an additional eight times the mass of water was added and stirred. After dehydration, the washed crushed material was dried at 50°C. Flakes from polyethylene terephthalate single-layer containers obtained using the same procedure were added to the crushed flakes, dry blended, and diluted twice. The dried pulverized material was extruded into strands using a twin-screw extruder (TEM26SX, manufactured by Toshiba Machine Co., Ltd.) at a heater temperature of 280°C and a discharge rate of 20 kg / hour, and the strands were cooled in a water tank while being cut into pellets using a pelletizer. Note that the gas barrier layer (polyethylene furanoate layer) was not separated by winnowing.

[0089] (Crystallization / Solid-State Polymerization Step) The pellets obtained in the granulation step were heated at 200° C. for 7 hours under a vacuum reduced to 1 Torr or less. The pellets after the heat treatment were taken out and used as recycled polyethylene terephthalate.

[0090] Examples 2 to 4 and Comparative Examples 1, 3 to 11 [Production of multilayer containers and recycled polyethylene terephthalate] Multilayer containers and recycled polyethylene terephthalate were produced in the same manner as in Example 1, except that the types and amounts of the phenolic antioxidant (A) and phosphorus-based antioxidant used in the polyethylene terephthalate resin mixture (polyethylene terephthalate layer, polyethylene terephthalate resin composition) in Example 1 were changed as shown in Tables 1 and 2. In Tables 1 and 2, the contents of the phenolic antioxidant (A) and phosphorus-based antioxidant are shown in "ppm" (parts per million by mass, ppm by mass). 1 ppm is 0.0001% by mass.

[0091] Example 5 [Production of multilayer container and recycled polyethylene terephthalate] A multilayer container and recycled polyethylene terephthalate were produced in the same manner as in Example 1, except that polyethylene furanoate was changed to polyglycolic acid.

[0092] Example 6 [Production of multilayer container and recycled polyethylene terephthalate] A multilayer container and recycled polyethylene terephthalate were produced in the same manner as in Example 2, except that in the preform molding of Example 2, injection molding was performed so that the mass proportions of the polyethylene terephthalate layer and the gas barrier layer were as shown in Table 1.

[0093] Comparative Example 2 [Production of multilayer container and recycled polyethylene terephthalate] A multilayer container and recycled polyethylene terephthalate were produced in the same manner as in Comparative Example 1, except that polyethylene furanoate was changed to polyglycolic acid.

[0094] [Evaluation Method] <Preparation of Evaluation Sample> The following haze, b * value and Δb * The evaluation samples of recycled polyethylene terephthalate for which the values ​​were measured were prepared as follows. The pellets after heat treatment of the Examples and Comparative Examples were injection molded into plates measuring 60 mm in length, 90 mm in width, and 3.0 mm in thickness using an injection molding machine (manufactured by Sumitomo Heavy Industries, Ltd., model SE130DU-HP) with an injection cylinder under the molding conditions shown below. Injection cylinder temperature: 280°C Mold cooling water temperature: 15°C Cycle time: 45 seconds

[0095] <b * The haze value of the evaluation sample was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7105:1981. * The value was measured. * The value represents the chromaticity. * is yellow direction, -b * represents the blue direction. * The absolute value of the value is small, and b * The smaller the value, the more suppressed the yellowing, the better the colorlessness and the better the color tone.

[0096] <Δb * The polyethylene terephthalate (Polyclear Refresh PET 1101) used as the raw material was molded under the conditions shown in <Preparation of Evaluation Sample> to produce a plate having a length of 60 mm, a width of 90 mm, and a thickness of 3.0 mm. Next, the haze was measured using a haze meter COH400 (manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7105:1981. * The values ​​were measured (b * Value 5.3). Above <b * The values ​​of the evaluation samples of the examples and comparative examples obtained * value and the b value of polyethylene terephthalate used as raw material * The difference in value (5.3) is Δb * The value was Δb * The smaller the value, the more the yellowing is suppressed, the less discoloration from the raw material polyethylene terephthalate occurs, and the more excellent the colorlessness is, which is preferable. * If the value is 0.8 or less, the colorlessness is good, and Δb * If the value exceeds 0.8, the colorlessness is poor.

[0097] <Haze> The haze of the plate was measured based on JIS K 7136: 2000 using a haze meter COH7700 (manufactured by Nippon Denshoku Industries Co., Ltd., white LED light source) and calculated as the average value of four measurements. The smaller the haze value, the better the transparency of the recycled polyethylene terephthalate, which is preferable.

[0098]

[0099]

[0100] As shown in Table 1, the recycled polyethylene terephthalate obtained by recycling the multilayer containers of the Examples has a low yellowness index, excellent colorlessness, and excellent transparency. Therefore, it is clear that the multilayer container of the present invention can suppress yellowing of the recycled polyethylene terephthalate obtained by recycling it, and that the recycled polyethylene terephthalate obtained by recycling also has excellent transparency.

Claims

1. A multilayer container having: a polyethylene terephthalate layer containing polyethylene terephthalate (X), a phenolic antioxidant (A), and a phosphorus-based antioxidant (B); and a gas barrier layer containing at least one resin (Y) selected from the group consisting of polyethylene furanoate and polyglycolic acid, wherein the phosphorus-based antioxidant (B) is a compound having a pentaerythritol skeleton and an aromatic ring, and the total content of the phenolic antioxidant (A) and the phosphorus-based antioxidant (B) in the polyethylene terephthalate layer is 0.050 to 0.220% by mass.

2. The multilayer container according to claim 1, wherein the content of the phenolic antioxidant (A) in the polyethylene terephthalate layer is 0.010% by mass or more.

3. The multilayer container according to claim 1 or 2, wherein the phosphorus-based antioxidant (B) is a compound represented by the following general formula (1): (In the formula, R 1 ~R 6 are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms.

4. The multilayer container according to any one of claims 1 to 3, wherein the mass ratio [(A) / (B)] of the content of the phenolic antioxidant (A) to the content of the phosphorus-based antioxidant (B) is 2 / 8 to 5 / 5.

5. A multilayer container according to any one of claims 1 to 4, wherein the content of the gas barrier layer is 0.05 to 15.0 mass % based on the total amount of the polyethylene terephthalate layer and the gas barrier layer.

6. The multilayer container according to any one of claims 1 to 5, wherein the bio-based content of the gas barrier layer is 90% by mass or more.

7. The multilayer container according to any one of claims 1 to 6, wherein the multilayer container is a hollow container.

8. The multilayer container according to any one of claims 1 to 7, wherein the multilayer container has a 3 to 5 layer structure, the outermost layer and the innermost layer being polyethylene terephthalate layers.

9. A method for producing recycled polyethylene terephthalate, comprising a step of recovering polyethylene terephthalate from the multilayer container according to any one of claims 1 to 8.

10. The method for producing recycled polyethylene terephthalate according to claim 9, wherein the polyethylene terephthalate recovery step is followed by one or more steps selected from a crystallization step and a solid-state polymerization step.

11. A method for producing recycled polyethylene terephthalate according to claim 9 or 10, comprising a step of washing the multilayer container or its pulverized product according to any one of claims 1 to 8 with an alkaline aqueous solution and recovering polyethylene terephthalate.

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